What is the test for a defendant who lacks malice in a murder case?

Under section 187, subdivision (a), murder is the unlawful killing of a human being with malice aforethought. A person who commits an intentional and unlawful killing but who lacks malice is guilty of voluntary manslaughter pursuant to section 192. The intent to kill generally constitutes malice. In limited and explicitly defined circumstances, a defendant who intentionally kills may lack malice when the defendant kills in unreasonable self-defense or when the defendant acts in a sudden quarrel or heat of passion. Neither heat of passion nor imperfect self-defense is an element of voluntary manslaughter that must be affirmatively proven. Instead, they are theories of partial exculpation reducing murder to manslaughter by negating the element of malice. (People v. Moye (2009) 47 Cal.4th 537, 549.)